Conventionally water boilers are commonly used in order to increase the temperature of water. Examples of water boilers include household furnaces, water heaters, and the like. A type of water boiler includes a generally cylindrical helically coiled finned heat exchanger tube surrounding an open center cavity containing a burner at one end and a core at the other end. Typically, the core has a flat top facing the burner--see for example the Silica Core U.S. Pat. No. 4,442,799--Heat Exchanger and/or the Aluminum Core U.S. Pat. No. 5,131,351--Heat Exchanger Plug. The water within the heat exchanger tube is available for thermal transfer from the gases passing thereby. The purpose of the burner is to provide products of combustion which, passing over the coiled heat exchanger tube, transfer heat thereto. The purpose of the core is to concentrate the flow of these products of combustion to the area immediately adjacent to the coiled heat exchanger tube so as to increase the efficiency of the heat transfer therebetween.
A difficulty of these water boilers is that they run at low temperatures on start up, particularly where the boiler is undersized for part of the operating time (i.e., lacks a tremendous reserve). These low temperature operations tend to produce contaminants, particularly on the exchanger adjoining the top of the core. This causes a residue buildup between the fins and increases back pressure while also reducing thermal transfer efficiency. Further, although set forth as sacrificial in U.S. Pat. No. 5,131,351, it has been ascertained that a patina develops on the surfaces of aluminum cores, which patina obstructs any corrosion of such core past a certain initial point.
The present invention is directed to improving the nature and construction of water boilers so as to increase the operational efficiency and service life thereof.